CatYou 2 PCS Dog Door Bells for Potty Training Housebreaking and Housetraining, Premium Quality Package Contain: 2 * Bells, 4 * screws. Use one bell for inside and the other one for outside. Easy to install, Each Bell come with two screws for easy installation, you can mount the bell on the door or wall. Easily and quickly train your dog to ring the bell when nature calls. The pleasant chime sound can be heard when your dog wants to go out or want potty. Premium quality, our bells are made out of Solid Metal guaranteed to never break. Your dog's nails can easily get caught in jingle type bells, Our Bell has No Dangerous Slots for nails to get caught in.